Method of forming an electroplatable microporous film with exposed metal particles within the pores

ABSTRACT

Rendering non-conductive substrates electroplatable by firmly bonding and uniting thereto an electroplate-receptive coating comprising a film-forming thermoplastic organic polymer and electrically conductive metallic particles having a largest dimension in the range of about 0.02 to 50 microns, the solids portion of the coating comprising at least about 20 percent by volume of a film-forming polymer and at least about 25 percent by volume of metallic particles, the coating further having a microporous structure to a depth of at least about 1 micron from the exposed surface thereof, and this microporous structure having about 40 to 90 percent open space, with the major portion of the open space being provided by pores with a largest dimension between about 0.1 to 15 microns, and with the metallic particles exposed in this microporous structure.

United States Patent [191 Cross et a1.

[ NOV. 27, 1973 J. Testa, Westwood, both of Mass; Ralph N. Thompson,Pittsburgh, Pa.

[73] Assignee: Amicon Corporation, Lexington,

Mass.

[22] Filed: Feb. 23, 1971 [21] Appl. No.: 118,090

Related U.S. Application Data [63] Continuation-in-part of Ser. No.661,555, Aug. 18,

1967, abandoned.

[52] US. Cl 117/227, 117/63, 117/160, 117/138.8 A, ll7/138.8 UA, 156/3,204/30,

[51] Int. Cl. B44d 1/18, C23f 17/00 [58] Field of Search 204/30, 38,2022;'

3,522,339 Ve1de 156/3 2,360,650 10/1944 Crane 156/2 3,466,232 9/1969Francis et a1. 204/30 3,014,818 12/1961 Campbell 117/138.8 3,259,5597/1966 Schneble et a1. 204/38 3,632,704 l/1972 Coll-Palages 117/47 AFOREIGN PATENTS OR APPLICATIONS 876,858 9/1961 Great Britain 204/Primary Examiner-Daniel E. Wyman Assistant Examiner-P. E. KonopkaAttorney- F. W. Furlong [5 7] ABSTRACT Rendering non-conductivesubstrates electroplatable by firmly bonding and uniting thereto anelectroplatereceptive coating comprising a film-forming thermoplasticorganic polymer and electrically conductive metallic particles having alargest dimension in the range of about 0.02 to 50 microns, the solidsportion of the coating comprising at least about 20 percent by volume ofa film-forming polymer and at least about percent by volume of metallicparticles, the coating further having a microporous structure to a depthof at least about 1 micron from the exposed surface thereof, and thismicroporous structure having about to percent open space, with the majorportion of the open space being provided by pores with a largestdimension between about 0.1 to 15 microns, and with the metallicparticles exposed in this microporous structure.

1 Claim, No Drawings METHOD OF FORMING AN ELECTROPLATABLE MICROPOROUSFILM WITH EXPOSED METAL PARTICLES WITHIN THE PORES This application is acontinuation-in-part of our copending application, Ser. No. 661,555,filed Aug. 18, 1967, now abandoned.

It has long been an object of the electroplating industry to provideeconomical, effective, and convenient means to coat or decorate avariety of non-metallic articles. In recent years the need for such aversatile process for use in electroplating a rapidly growing variety ofplastics has become more acute. Nevertheless, until the instantinvention, all processes available in the art were severely limited intheir utility, typically by one or more of the following factors:

1. poor adhesion of the electroplated coating to the non-conductivesubstrates;

2. utility with only a very few special plastics as substrates;

3. necessity of using a great number of processing steps to get thesubstrate ready for electroplating, typically about nine distinct steps;and

4. poor appearance, e.g., insufficient smoothness or uniformity on theresulting coated product.

Thus it is an object of the present invention to provide a simpleprocess for electroplating non-conductive structures which processallows the choice of any of a large number of non-conductive materialsfor fabrication of the article to be electroplated. I

It is a further object of the invention to provide novel primingcompositionsuseful in the process of the invention.

Another object of the invention is to provide novel articles ofmanufacture which are susceptible of convenient electroplating. I

A still further object of the invention is to provide novelelectroplated articles of manufacture having a strongly-bonded metalliccoating of excellent appearance.

Other objects of the invention will become obvious to those skilled inthe arton reading this specification.

The invention features applying to. an electrically non-conductive 1substrate a A novel electroplatereceptive coating firmly bonded andunited to the substrate. This coating comprises 'a film-formingwaterinsoluble thermoplastic organic polymer and electrically conductivemetallic particles having a largest dimension in the range of about 0.02to 50 microns. The solids portion of the coating is at least about 20percent by volume of the film-forming thermoplastic organic polymer andat least about 25 percent by volume of the electrically conductivemetallic particles. The coating has a microporous structure to a depthof at least about 1 micron from the exposed surface. This microporousstructure has about 40 to 90 percent (preferably, about 75 to 90percent) open space, and the major portion of the open space is providedby pores with a largest dimension between about 0.1 to 15 microns, withthe conductive metallic particles being exposed in the coat- Inpreferred embodiments, the solids portion of the coating is about to 80percent by volume of metal particles of which at least the major portionby weight has a largest dimension between about 1 and 10 microns. Wherethe coating is sufficiently thick, the microporous structure may extendto a depth of 10 microns or even more to provide a particularlyreceptive coating. The coating is preferably open-celled in themicroporous portion with substantial interconnection between pores.

The coating may be applied in any total thickness, so long as it has themicroporous structure described at its exposed surfaces. Such coatingsare generally applied in thicknesses ranging from 0.1 to 20 mils.

It is usually desirable to subject the coated substrate to aconventional preplating step before preceding with the conventionalelectroplating procedure. This preplating is accomplished in arelatively high-acid preplate bath. Normally a chemical displacementtype preplate suffices; the metallic atoms from the preplate bathdisplace atoms of the conductive filler and thus avoid unnecessarycontamination of the electroplating bath with ions of the conductiveparticles. Moreover, a more strongly adherent electroplate coat appearsto result from use of the preplate step.

In general, the preplating step is used to reduce the electricalresistance of the coating on the substrate before it issubjected to theusually electroplating procedure. For example, coatings comprising tinpowder have very little conductivity until the preplate step is carriedout thereon. The preplate step will normally increase the conductivityof the surface until it has a surface resistivity of less than about1,500 ohms/square as measured with a Triplett Electronic Volt-Ohm meter,Model 850. The preplate step allows use of coatings having very little,indeed almost no initial electrical conductivity, and is convenientlycarried out at 20 to 30C for from 2 to 5 minutes in a sulfuric acid bathcomprising 188 grams of CuSO 148 grams of H and 1,000 grams of water.However, fairly broad changes in the sulfuric acid and copper-ionconcentrations can be tolerated.

Among the useful film-forming water-insoluble thermo-plastic organicpolymers forming the coatings of the present invention are polyvinylacetate, polyvinyl butyrate, polyvinyl chloride, polyvinyl fluoride,polycarbonate, polyvinyl butyral, polyvinylalcohols (e.g., highmolecular weight (10 or greater) or crosslinked), polyvinyl methylether, polyvinylidene chloride, poly-vinylidene fluoride,water-insoluble divalent salts of carboxy-methylcellulose,polyurethanes, polyacrylonitrile, polysulfones, polyarylsulfones,polymethyl methacrylate, cellulose acetate and the like. Other suchpolymers include various copolymers such as polyvinyl chloride-polyvinylacetate, polyvinyl chloride-polyacrylonitrile, poly(acrylonitrile-butadienestyrene) copolymers and the like.

Those skilled in the art, on perusing the above list and reading theinstant-specification, will realize that the polymers are utilizedmanipulatively and any polymer can be utilized providing thatfilm-forming coatings of the polymer can be prepared to provide themicroporous substrate desired for suitable electroplating; and providingfurther that the polymer has sufficient adhesive affinity for thenon-conductive substrate to adhere thereto or can be dissolved ordispersed in a liquid in which the non-conductive substrate has a degreeof solubility. In this latter circumstance, a sufficiently strongadhesive. bond can be induced between the non-conductive substrate andthe microporous precoat to satisfy the requirements of the invention.

For preparing most of the non-conductive substrates for electroplatingaccording to the invention, the relatively polar film-forming organicpolymers known to the art are entirely satisfactory and indeedadvantageously utilized because of the wide selection of solvents inwhich they can be suitably dissolved.

Since, with the described novel coatings, any failure of theelectroplate, in terms of peel strength, will take place not at theelectroplate-coating interface, but within the microporous structure ofthe applied coating; peel strength can be largely controlled byselection of a polymer of desirable strength.

Among the electrically conductive metallic particles that are useful inthe coatings of the invention are those formed of the metals copper,tin, nickel, silver, iron, lead, cadmium, chrome, zinc, and mixtures andalloys of these with each other, and the like.

These particles should have a largest dimension in the range of about0.02 to 50 microns. The smaller sizes are preferred when high-glossplating is to be carried out; larger particle sizes are preferred forless glossy, e.g. satin finish coatings. They can be of any shape, forexample spherical or acicular shapes such as chain-like or flake-likeconfigurations.

Particularly advantageous are electrically conductive particles ofchained or highly-structured configuration. This configuration may takethe form of a chaintype agglomerate structure; similar to the well-knownstructure of such generally electrically non-conductive particles aspyrogenic silica and pyrogenic alumina. These electrically conductiveparticles are characterized by having a ratio of exposed surface area toweight, prior to being incorporated into the coating, in the range ofabout 500 to 1,500 or more cm lgm, many times the surface area to weightratio of a spherical particle of equal weight. Preferably the majorportion by weight of such particles in the coating have a largestdimension in the range of about 1 to 5 microns. Illustrative of suchparticles is the chain-type conductive nickel powder sold under thetrade designation Type 255 Carbonyl Nickel Powder by The InternationalNickel Company, Inc. The major portion by weight of this powder is madeup of particles having an average largest dimension in the range ofabout 2.5 to 3.5 microns. These 2.5 to 3.5 micron particles are composedof primary particles chained into the larger agglomerate paticles. Theapparent density of this powder is about 0.5 to 0.6 grams per cc, withan exposed surface area to weight ratio estimated to be about 1000 cm/gm. Typical non-structured carbonyl nickel powders have an apparentbulk density at least about 70 to 500 percent greater than that of theType 255 nickel mentioned above. This is so even when there is nosubstantial difference in the size of the particles being tested forapparent bulk density.

Of less structured conductive fillers, a tin powder sold under the tradename MD 105 by Alcan Metal Powders, Inc. has been discovered to behighly advantageous.

Preferred methods for providing this microporous coating includeevaporation and leaching. According to the evaporation method, a liquidcomposition is prepared comprising a solution of the film-formingpolymer in a suitable solvent (preferably, about 9 to 25 percent polymerby volume), and metallic particles admixed with the solution. Therelative proportions of polymer and metal particles are preferably about20 to 50 parts (by volume) polymer to about 80 to 50 parts (by volume)particles, based on the total volume of polymer and metal particles. Inaccordance with the evaporation process, this liquid composition isapplied to the substrate, and the solvent is evaporated at a temperaturebelow its boiling temperature, yet at a rate sufficient to provide ablushed surface on the coating, to a depth of at least about 1 micron.Low boiling solvents (below about 80C) with substantial vapor pressures(100 mm or more) below about C are particularly useful. Although thechoice of solvents depends largely, of course, upon the polymer to bedissolved, useful solvents for polar polymers include acetone, methylacetate, ethyl acetate, tetrahydrofuran, methylene chloride, chloroform,methanol, ethylene dichloride and the like. Those skilled in the artwill, on reading the above list, realize that a broad spectrum ofsolvents can be utilized and will be able to select a solvent suitablefor their own conditions.

According to the leaching process, there is applied to the substrate aliquid composition comprising a solution of a film-forming thermoplasticorganic polymer containing conductive metallic particles having alargest dimension in the range of about 0.02 to 50 microns, and aleachable component. Preferably, the volume of polymer is 20 to 50percent and the volume of metal particles is 80 to 50 percent, based onthe total volume of polymer and metal particles. The polymer volumeshould be 9-25 percent based on the total volume of solution plusleachable component (but excluding metal). The leachable component is amaterial which is soluble in a solvent or wash liquid which itself is anon-solvent for the polymer and metal. The composition is thenevaporated to leave about 50 to 250 percent by volume of the leachablecomponent, based on the volume of film-forming polymer. This partiallycomplete coated substrate may (particularly if the leaching component isnon-volatile) be maintained in this state until it is desired to finishmaking the coating. Then, the coated substrate containing the leachablecomponent is exposed to the aforesaid solvent to remove this component,leaving a microporous structure in the applied coating. As will beevident, the leachable component may in some cases be a portion of thesolvent in which the polymer is dissolved and in which the filler isslurried. Or it may be another liquid or a solidpreferably, awater-soluble solid.

Among materials which can be suitably incorporated into the coatingcomposition as a leachable component are various inorganic and organicmaterials such as the water soluble salts of alkali and alkaline earths,including sodium bromide, potassium iodide, magnesium nitrate, calciumbromide, zinc chloride, barium chloride,

- cadmium nitrate, and the like. Other suitable watersoluble salts suchas the soluble sulfates, nitrates, chlorides, perchlorates and the likeare suitable, including e.g., copper sulfate, aluminum chloride,aluminum sulfate, ammonium nitrate, ammonium chloride, and ammoniumsulfate. Other leachable materials include the water-miscible organicand inorganic liquids. For example, ethanol, dioxane, acetone, 2-butoxyethanol, glycerine, dimethylformamide, ethyl acetate, dimethylsulfoxide, ethylene glycol, propylene glycol, and the like are useful inthe process of the invention, as are soluble organic solids such ascarbohydrates like carboxymethyl-cellulose and acid-decomposablematerials such as calcium carbonate and the like. It if often mostconvenient to allow a portion of a solvent used in forming the coatingcomposition to stay in the coating after the evaporation step to serveas part or all of the leachable component thereof.

These leachable materials, too, are chosen primarily for their physicalproperties, and hence any material having the required solubility.characteristics (and which, of course, is not otherwise reactive withthe coating composition) can be used.

The wash liquid for reasons of safety and economy will usually be water.Were one to select a more exotic wash liquid and incorporate a leachablecomponent into the coating composition of the invention which would besuitable leached by this exotic fluid, the requirements of the inventionwould still be satisfied.

In some embodiments within the scope of the invention it is possiblethat long-term deterioration of the microporous polymeric film can becaused by degradation of the film-forming polymer caused by thecatalytic action'of the metal ions resulting from interaction ofresidual moisture and the conductive fillers. In such situations use ofa less polar wash fluid than water, for example ethanol, is indicated.

In most circumstances the surfaces of the nonconductive materials to beprepared for electroplating according to the process of the inventionwill adhere readily to the microporous precoat comprising the conductivefillers of the invention. This adherence will in some cases be primarilymechanical, as for example when a rough cement or ceramic substrate iscoated. In some situations however, a chemical or mechanical treatmentof the non-conductive surface will assure an optimum bond between thesurface and microporous coating applied thereto. In one such case, thepretreatment with chlorosulfonic acid and sulfuric acid of an article ofwood-flour-filled phenolic resin substrate sold under the trade nameBM-5000 by Union Carbide Corporation, resulted in increased bondingstrength of electroplates, applied according to the invention, by aboutpercent.

Exemplary of the substrate materials receptive to such coatings arepolystyrene, polymethyl methacrylate, acrylonitrile-butadiene-styrenecopolyrners, phenolic resins, and'polydiallyl phthalate.

Moreover, for higher temperature applications, such heterocyclic,nitrogen-containing polymers as polyimides, polyamide copolyrners,polyirnidazolines, polyimidazoles and polyirnidazolones are usefulnonconductive polymeric substrates. Polybenzimidazole is an example ofsuch a polymer.

The following examples are presented to illustrate the process of theinvention and some of the novel products produced thereby. Theseexamples are not intended to be limiting and various changes inconditions, proportions, and components can be made to fit theparticular purposes of any skilled in the art.

EXAMPLE 1 Process A solution was prepared comprising one part by weightof film-forming polymer, a polyvinyl acetate available under the tradedesignation LEMAC1,000 from the Borden Chemical Company, and 9 partsN,N'-dimethylformamide (DMF) solvent. Then, 19 parts of a conductivefiller, a spherical tin powder of about 1.5 microns in average particlediameter and available under the trade designation MD 105, from AlcanMetal Powders Incorporated, was mixed under high shear into thesolution, thereby forming a slurry which was a coating compositionaccording to the invention.

The resulting slurry was coated on a polystyrene article. A film coating0.1 mil thick was applied to the preconditioned polymer surface by meansof a Gardner drawdown bar. The slurry and substrate temperatures wereboth about 25C during this coating step.

The film coating was partially dried in an aircirculating oven at C.This partial drying" removed all but about 15 percent of the solventfrom the tin-polyvinyl acetate coating. Residual solvent was leachedfrom the coating by submersing the coating in an agitated water bath forabout 10 minutes at 30 to 35C.

After being coated as shown above, the precoated polystyrene substratewas electroplated by l. immersion in an acid copper sulfate solution,i.e. a pre-plating bath containing 188 grams CuSO 148 grams H and 1,000grams of water, to form a thin coating of copper on the exposed tin by achemical displacement reaction. Submersion time was 10 minutes.Temperature of the bath was about 28C.

2. electroplating in a typical electrolytic plating bath comprising 188grams of CuSO, and 74 grams of H 80, per 1,000 grams of water. Thiselectroplating was carried out at about 28C for 60 minutes using acurrent density of 12 amps/ft? The final electroplated coating was about0.001 inch'thick.

Testing for strength of electroplate-plastic bond The metal layer andmicroporous precoat on a coated plastic plaque prepared as describedabove were cut to form distinct electroplated strips one inch wide andabout 2 inches long. About one-half inch of this strip was peeled backand a reinforcing tape was attached to both sides of the strip which hadbeen peeled back. Thus prepared, the test specimens were conditioned for4' hours at 70F and 50 percent relative humidity.

The plaques are then mounted on a tensometer. One grip of the tensometeris attached to the reinforcing tape and a second grip holds the plaquein such a way as to maintain the angle of pull on the peeled-back stripof electroplated metal at with respect to the electroplated surface ofthe plaque. The grips are caused to separate at a rate of 1 inch perminute until the entire metal strip is separated from the plastic. Thepeel strength is taken as the mean tensile value required to peel this 1inch wide strip from the plaque. Normally several such mean values areaveraged to obtain a reliable test result.

When the peel strength of the electroplated article of Example 1 wastested, it was found to be 3.2 lbs. per linear inch.

Effect of amount of solvent remaining in the coating after the wash stepThe foregoing procedure was repeated several times, to establish theeffect of evaporation of different quantities of solvent from theprecoat before the leading step. The following results were obtainedwith amount of residual solvent by volume based on the volume of polymersolids.

% Rsidual Solvent (i.e. no drying It is apparent that residual solventquantities of between about 50 and 300 percent by volume based on thevolume of polymer solids are advantageous. These quantities are believedto be proportional to the porosity of the leached precoat.

Effect of varying polymer substrates:

Substantially the same results were obtained when (a) anacrylonitrile-butadiene-styrene copolymer available under the tradedesignation EP3510 from Marbon Chemical Division of Borg WarnerCorporation, (b) a polymethyl methacrylate polymer available under thetrade designation Plexiglas from Rohm & Haas Company, (c) a phenolicresin available under the trade designation BM-5000 from Union CarbideCorporation, (d) a polystyrene available under the trade designation KPD901 from Sinclair-Koppers Company, and (e) a polydiallyl phthalateavailable under the trade designation 51-01 from Allied ChemicalCorporation, were coated and electroplated according to the detailedprocedure of coating and electroplating the polystyrene article of theinstant example.

The aforesaid phenolic substrate was etched with chlorosulfonic acid forthree minutes at 30C before use.

EXAMPLE 2 The procedure of Working Example 1 was repeated except thatthe film-forming polymer was one part of polyvinyl chloride-polyvinylacetate copolymer of the type available under the trade designation VYHHfrom B. F. Goodrich Company and the conductive filler was a flake-shapedcopper powder and sold under the trade designation 1109 by ValleyMetallurgical Processing Co. The article coated and plated was ofacrylonitrilebutadiene-styrene copolymer.

Peel strengths of about 2.5 lbs. per inch were obtained. As was alsotrue with test specimens of Example 1, failure was noted to take placewithin the matrix of the porous precoat rather than at the microporouscoating-plastic article or microporous coatingelectroplate interfaces.

EXAMPLE 3 The procedure of Working Example 1 was again repeated, thistime using a film-casting slurry of 1 part polycarbonate of the typesold under the trade designation Lexan 141 by General Electric Company,19 grams of the tin powder used in Example 1 and 9 grams ofethylacetate. When coated, dried, and leached on an article formed ofpolycarbonate, a peel strength of 3.1 lbs. per linear inch was attained.

When a non-porous precoat was used, i.e., when all or very nearly all ofthe solvent was evaporated from the precoat before it was washed inwater, a peel strength of only 1.3 lbs. per linear inch was realized.

EXAMPLE 4 Again using the procedures set forth in Working Example I, onepart by weight of the sodium salt of a carboxymethyl-cellulose gumavailable under the trade designation 7M from Hercules Incorporated wasdissolved in ethanol, and 10 parts of copper used in Working Example 2was dispersed therein to form a coating composition according to theinvention. The slurry was coated onto a polystyrene substrate, which wasthen immersed in a 1 molar solution of copper sulfate at roomtemperature for about five minutes to form the water-insoluble divalentcopper salt of carboxymethylcellulose. The peel strengths ofsubsequently electroplated coatings on the thus coated substrate were,again, found to be improved. Peel strengths of about 3 lbs. per inchwere obtained.

EXAMPLE 5 One part by weight of polyvinyl butyral, available under thetrade designation, BUTVAR 76 from Monsanto Company, and 19 parts byweight of a spherical tin powder, available under the trade name MD 105from Alcan Metal Powders Incorporated, were slurried in 5 parts of asolvent consisting of equal parts by weight of DMF and dimethylsulfoxide(DMSO). The resulting coating composition was coated onto a surface of apolymethyl methacrylate article and allowed to dry for 3 minutes at 65Cbefore being leached for 30 minutes in a water bath at 60C. On beingelectroplated according to the process described in Example 1, aninitial peel strength of about 2.5 lbs. per inch was realized.

EXAMPLE 6 Compounding and Coating:

A general procedure is set forth herein. The specific quantities andkinds of conductive fillers used and the peel strengths obtainedtherewith are set forth in Table I. A solution was prepared comprisingone part by weight of film-forming polymer, a polyvinylacetate (PVA)polymer available under the trade designation LEMAC-lOOO from the BordenChemical Company, and 9 parts of ethyl acetate. Then, a conductivefiller was mixed under high shear into the solution, thereby forming aslurry.

The resulting slurry was coated on the acrylonitrilebutadiene-styrenecopolymer plaque. A film coating 0.1 mil thick was applied to thenon-conductive surface by means of a Gardner drawdown bar. The slurryand substrate temperature were both about 25C during this coating step.

The film coating was dried in an air-circulating oven at 65C for about 6minutes in which time substantially all the solvent was removed. (Thistemperature was found to provide a sufficiently fast evaporation ofethyl acetate to provide micro-porosity but such evaporation was at asufficiently moderate rate to avoid cracking of the precoat surface asit dried).

The electroplating and peel-strength testing steps were carried out ashas been set forth above in Example 1.

Precoat Slurry Composition Run 1 Run 2 3 Run 4 a. PVA Solution (parts byweight) l0 l0 10 10 b. Nickel, structured (parts by weight) 8 4.0 0.8 0c. Tin

(parts by weight) 0 4.0 7.2 10 Peel Strength 4.8 6.7 7.0 2.4

As will be evident from the foregoing table, the higher peel strengthswere obtained with mixtures of the spherical and highly-structuredfillers. However, in all cases where the highly-structured filler wasused very high peel strengths were achieved compared to those achievedin Examples l-5.

EXAMPLE 7 Compounding and Coating:

Two solutions were prepared comprising 700 gms film-forming polymer, apolyvinylacetate (PVA) polymer available under the trade designationLEMA- C-lOOO from the Borden Chemical Company, and 7,000 gms of ethylacetate. Then, a conductive filler consisting of 5,600 gms of nickel(same as Example 6) and 320 gms of tin (same as Example 6) was mixedunder high shear into the solution, thereby forming a slurry.

A 50 micron thick coating of each resulting slurry was coated on bymeans of a Gardner drawdown bar. The slurry and substrate temperaturewere both about 25C during this coating step.

One film coating was dried in an air-circulating oven at 65C for about 6minutes and the other at room temperature (about 25C) overnight.

The microporosity of each dried coating was photomicrographicallyobserved to extend to a depth of about 10 microns and to be about 70 to80 percent open space, with the major portion of the open space providedby pores ranging in size from 1 to microns, although pores down to the0.1 micron range were also observable.

Other embodiments will occur to those skilled in the art and are withinthe following claims.

What is claimed is: 1. A process for preparing a surface of anonconductive substrate for reception of an electroplated coating 5comprising the steps of applying to said substrate a compositionconsisting essentially of a solution of a film-forming waterinsolublethermoplastic organic polymer in a solvent which is itself soluble inwater, and mixed therewith electrically conductive metal particleshaving a largest dimension in the range of about 0.02 to 50 microns,said polymer occupying about 9 to 25 percent of the total volume ofsolution exclusive of said metal particles, saicl polymer and said metalparticles being present in a ratio of to 50 percent by volume of polymerto 80 to 50 percent by volume of metal particles based on the totalvolume of polymer and metal particles, evaporating said solution toleave a coating containing about 50 to 250 percent by volume of saidsolvent based on the volume of said film-forming polymer, and applyingwater to said coating to remove said solvent to form a coating having amicroporous structure having about 40 to 90 percent open space, withsaid metal particles being exposed within the pores.

